1. (Field of Invention)
The present invention relates to a die for use in forming optical lenses made of glass or synthetic resin used in OA (office automation) instruments, VTR (video tape recorder), cameras and the like and aims at the prolongation of a useful life of the die by suppressing the oxidation or deterioration of the die surface due to temperature and atmosphere and reaction or wear caused by friction of materials, of which lenses are made, when lenses are formed.
2. (Prior Art)
Optical lenses have been formed by the lapping method using an inefficient pitching device. That is to say, lenses have been formed one by one, in particular nonspherical lenses have been finished by skilled manual operation with repeated workings and measurements.
On the contrary, a forming method using a metal die has been increasingly utilized as a mass production method in place of the conventional grinding method and polishing method since (1) it is higher in productivity; and (2) the products show less nonuniformity in quality in comparison with the conventional methods.
However, since the shape and accuracy of the surface of optical lenses used in OA instruments, VTR, cameras and the like are measured with wave length of lights as a standard, the working of optical lenses requires a remarkably high accuracy.
Accordingly, in the event that optical lenses are produced by the forming method, the roughness of the surface of the metal die requires high accuracy in addition to a high dimensional accuracy for cavities and cores of the metal die in respect of the transferring property thereof.
The above described forming method has a problem in a useful life of metallic materials.
Although the operation condition of a metal die is dependent upon materials of lenses to be formed, a metal die is usually used in an oxidizing atmosphere at high temperatures, so the accuracy of the surface of a remarkably expensive metal die is reduced within a comparatively short period of time owing to the oxidation and deterioration of the surface of the metal die, chemical reactions between glass and the metal die and the like, thereby losing its usefulness.
On account of the above described, the price of optical lenses has not been reduced.